<template>
  <h3>小星星跟随鼠标</h3>
  <span class="js-cursor-container"></span>
</template>

<script>
export default {
  name: "index",
  methods:{
    show(){
      (function fairyDustCursor() {

        var possibleColors = ["#D61C59", "#E7D84B", "#1B8798"]
        var width = window.innerWidth;
        var height = window.innerHeight;
        var cursor = { x: width / 2, y: width / 2 };
        var particles = [];

        function init() {
          bindEvents();
          loop();
        }

        function bindEvents() {
          document.addEventListener('mousemove', onMouseMove);
          window.addEventListener('resize', onWindowResize);
        }

        function onWindowResize(e) {
          width = window.innerWidth;
          height = window.innerHeight;
        }

        function onMouseMove(e) {
          cursor.x = e.clientX;
          cursor.y = e.clientY;

          addParticle(cursor.x, cursor.y, possibleColors[Math.floor(Math.random() * possibleColors.length)]);
        }

        function addParticle(x, y, color) {
          var particle = new Particle();
          particle.init(x, y, color);
          particles.push(particle);
        }

        function updateParticles() {

          for (var i = 0; i < particles.length; i++) {
            particles[i].update();
          }

          for (var i = particles.length - 1; i >= 0; i--) {
            if (particles[i].lifeSpan < 0) {
              particles[i].die();
              particles.splice(i, 1);
            }
          }

        }

        function loop() {
          requestAnimationFrame(loop);
          updateParticles();
        }

        function Particle() {

          this.character = "*";
          this.lifeSpan = 120; //ms
          this.initialStyles = {
            "position": "fixed",
            "display": "inline-block",
            "top": "0px",
            "left": "0px",
            "pointerEvents": "none",
            "touch-action": "none",
            "z-index": "10000000",
            "fontSize": "25px",
            "will-change": "transform"
          };

          // Init, and set properties
          this.init = function (x, y, color) {

            this.velocity = {
              x: (Math.random() < 0.5 ? -1 : 1) * (Math.random() / 2),
              y: 1
            };

            this.position = { x: x + 10, y: y + 10 };
            this.initialStyles.color = color;

            this.element = document.createElement('span');
            this.element.innerHTML = this.character;
            applyProperties(this.element, this.initialStyles);
            this.update();

            document.querySelector('.js-cursor-container').appendChild(this.element);
          };

          this.update = function () {
            this.position.x += this.velocity.x;
            this.position.y += this.velocity.y;
            this.lifeSpan--;

            this.element.style.transform = "translate3d(" + this.position.x + "px," + this.position.y + "px, 0) scale(" + (this.lifeSpan / 120) + ")";
          }

          this.die = function () {
            this.element.parentNode.removeChild(this.element);
          }

        }

        function applyProperties(target, properties) {
          for (var key in properties) {
            target.style[key] = properties[key];
          }
        }

        if (!('ontouchstart' in window || navigator.msMaxTouchPoints)) init();
      })();
    }
  },
  mounted() {
    this.show()
  }
}
</script>

<style scoped>

</style>
